In view of the unique composition of hair fibers and the various changes in styles and fashion, the waving of hair has long been of particular interest. In order to best understand the various methods in which hair fibers can be styled or waved, it is important to remember that normal hair has three major bonds that hold the configuration of the hair and are responsible for the strength of the hair. These three bonds are salt linkages, hydrogen bonds, and disulfide bonds.
As is well known, hair is a protein produced from units known as "amino acids". A high proportion of these are diamino and dicarboxylic "amino acids", and thus the hair fiber is amphoteric in character. Since the number of free acid and basic groups are approximately equal, the hair's mechanical properties, such as its strength, is at its maximum at neutrality (pH 7). For example, the fiber becomes easier to stretch as the pH increases or decreases from pH 7. The cohesion of hair is also demonstrated by the minimum swelling in water at neutrality.
Because they are so numerous, the hydrogen bonds, involving the amino hydrogen and carbonyl oxygen of the amide linkages, are most important. Water, particularly in the monomolecular state, as occurs with moisture in the air (humidity), can weaken these bonds, by becoming a part of a hydrogen bonding structure. However, some of these hydrogen bonds are protected by hydrophobic bonds and will remain even when the hair is wet with water. More powerful hydrogen bond breakers, like high concentration of lithium bromide and urea are required for complete breakage of all hydrogen bonds.
As long as the hair fiber is dry, the strength of the hair fiber is not reduced. For example, a straight hair, wet with water and held by mechanical force in a curly configuration while drying will remain in a curly shape due to the formed hydrogen bonds and salt linkages, and it will not return to its straight shape so long as it remains dry. However, unless mechanically restrained, upon being wet with water, the hair will lose its curly configuration and become straight.
Furthermore, when hair is set by the use of water alone, the hair will gradually lose its curly shape through the absorption of atmospheric moisture and the resulting rearrangement of the hydrogen bonds. This is due to the fact that in water, the dominant bond is disulfide bond, while in the dry state, the dominant bonds are the salt linkages and the hydrogen bonds.
In regard to the disulfide bonds, hair is composed of a unique protein material called "keratin", which is distinguished by the fact that it contains a very significant amount of an amino acid (cystine) which contains the element sulfur in addition to the elements nitrogen, oxygen, carbon and hydrogen. In the natural synthesis of hair, the element sulfur covalently links adjacent polypeptide chains (K) through two sulfur atoms (S-S) to give keratin protein (K-S-S-K). Only by chemical action can this covalent linkage be broken.
Similarly, it is well established that in order to permanently wave hair, this disulfide linkage must be broken. In this regard, many prior art compositions have been developed for the "cold permanent waving" of hair. Typically, these prior art systems treat the hair with reducing agent which breaks the disulfide (cystine) linkage in the hair while the hair is wound around a curling rod. These prior art systems are typified by the disclosures in U.S. Pat. Nos. 2,479,382, 2,577,710, 2,577,711, 2,688,972, and 2,708,940.
It is believed that certain hydrogen bonds are protected by the cystine bond and are only broken by water when the cystine bond is split into two cysteine moieties. By the same rationale, these hydrogen bonds are re-formed in the new configuration and protected by the newly formed cystine bonds created in the neutralization step of permanent waving. In effect, these protected hydrogen bonds supplement the disulfide bonds in creating permanency to the new curl configuration.
In general, permanent hair waving is usually carried out by subjecting the hair to reagents containing a free --SH group or thiol. These materials are also called mercaptans. In this treatment, the hair is usually first wound on rollers and the saturated with the thiol. The thiol waving agent acts to break the disulfide bonds within the hair fiber forming thiol groups in the hair protein and disulfide bonds between two thiol waving agent molecules. The chemistry involved in the reaction of the mercaptan with the cystine disulfide bonds in the hair fiber is illustrated by the following chemical equation: EQU KSSK+2RSH.revreaction.2KSH+RSSR
When a sufficient number of hair disulfide bonds have been broken, the hair is realigned to pair previously unpaired hair protein thiol groups opposite each other. At this point, the hair is rinsed, removing the unreacted thiol waving agent and disulfide reaction product formed from it. Then, the hair is saturated with an oxidizing agent, or neutralizer, such as hydrogen peroxide or bromate salt, to reform disulfide bonds between the newly paired hair protein thiols, thereby giving the hair a new configuration or wave, or adding curl to the hair. By rebonding the sites of the reduced keratin in their new curled configuration, a permanent set which is impervious to water is established.
The rebonding of the reduced sites accomplished by the action of the chemical oxidizing agent is illustrated by the following chemical reaction: EQU 2KSH+H.sub.2 O.sub.2 .fwdarw.KSSK+2H.sub.2 O.
In spite of the substantial effort that has occurred in the development of various permanent waving compositions of this general nature, there has been a general inability to improve the holding power or curl configuration retention of "cold permanent waving" formulations. The typical problem encountered with the use of mercaptan reducing agents for the permanent waving of hair is that the permanency of the curl will not last until it is cut off. Instead, the curl relaxes slowly from the normal wear and tear of every day hair care. In this normal grooming process of shampooing, combing, drying and brushing the hair, the fibers are constantly being put under tension and exposed to forces that oppose the new disulfide and hydrogen bonds that were created in the new curl configuration.
In addition to longer curl retention, the industry has also sought to increase the luster, sheen, gloss and manageability of the hair, as well as provide a permanently waved head of hair which is soft, supple, and possesses a natural feel. However, these goals have not been fully attained.
Therefore, it is principal object of the present invention to provide a "cold permanent waving" formulation which imparts to the permanently waved head of hair a substantially increased lasting and curl retention ability.
Another object of the present invention is to provide a "cold permanent waving" formulation having the characteristic features described above which also imparts to the permanently waved head of hair a high luster, gloss, sheen and improved manageability.
Another object of the present invention is to provide a "cold permanent waving" formulation having the characteristic features described above which also imparts to the permanently waved head of hair a full-bodied appearance which is easily managed and feels soft and silky.
Other and more specific objects will in part be obvious and will in part appear hereinafter.